This invention relates to plain bearings having slide layer alloys based on copper-lead-tin, and more particularly to bearing laminates which have metallic supporting bodies.
It is already known to provide white metal bearing alloys based on a lead-tin-copper content in which up to 6% copper by weight is considered to be optimal. White metal bearing alloys have subsequently been suggested, wherein the copper content can be as high as 10% by weight with improved results.
In contrast to the foregoing, plain bearings having slide layer alloys of copper-lead-tin content, wherein a considerably higher percentage by weight of copper is utilized are frequently produced, these being known as bronze alloy bearings.
In foundry technology, bronze bearing alloys of this type are produced with a lead content of up to about 40% by weight, the lead distribution being coarse in part, due to dissociation processes, whereby their production presents a number of problems. Below 25% of lead, however, a relatively uniform bearing alloy structure is obtainable by casting, generally without difficulties. According to experience, low tin contents are used in such alloys; in isolated cases up to about 4%. Beyond this, lead-tin bronzes with decreasing lead content and increasing tin content are also being produced, by casting. For example, alloys with about 17% lead and 5% tin, or with 10% lead and 5% tin or with 10% lead and 10% tin are being frequently used.
However, there is an ever-increasing demand to inexpensively produce alloys of higher quality sliding properties, i.e. with a higher lead content while still retaining a uniform structure, but this has invariably met with foundry-related problems. One solution involved the development of sinter alloys. In such sintering of bearings, a copper-lead powder producing a finish alloy was used first, having as a limit for practical applications a lead content of approximately 35%. Here again, higher lead concentrations were subject to dissociation action during the sintering. In connection with this same problem, a bronze alloy having approximately 49% copper, 1% tin and 50% lead was developed, by producing a so-called impregnated sinter alloy. The procedure in producing the impregnated sinter alloy is such that a porous layer resembling a sponge is first sintered onto a metal base or carrier strip, by sintering copper powder and tin-bronze powder, and then this porous layer is impregnated with lead or a lead-tin alloy in a reducing atmosphere. There was also produced similar material, made by impregnating a porous sintered-on layer consisting of copper and nickel, with an alloy of lead having additives of tin and antimony. The total weight content of the lead, tin and antimony amounted to about 40%. In some cases, the impregnated sinter alloy layers are provided additionally with a covering layer of the impregnating alloy, to improve the slide properties.
The suitability of such bronze alloys, intended in particular for plain or slide bearings, can generally be described as follows:
Those alloys which are produced by casting are usually of satisfactorily high mechanical strength, but if they are not provided with additional slide layers, the inherent slide properties limit their application to moderate sliding speeds. In addition, at high lubricant temperatures, such alloys are susceptible to corrosion. The strength of these alloys decreases with a lead content above 25% because of the occurrence of lead liquations in the structure; at the same time, their susceptibility to lead corrosion in oil which has aged, automatically increases. Therefore, in heavy-duty multi-layered plain bearings, the foregoing bronze alloys are used almost exclusively in intermediate layers. The same applies to only sintered, lead-bronze constituted of finish-alloyed powder, where the mechanical strength is basically already lower, but where the susceptibility to liquation at higher lead contents is also lower, as well.
The impregnated sinter alloys have a coarse structure as compared to the sinter-bronze alloys described earlier, but due to their special structure, their stength is favorable considering their high lead contents. The coarse structure, possibly with the simultaneous use of tin-less impregnating alloys, results in an increased susceptibility to lead corrosion due to old or aged oils, particularly at elevated temperatures, and additionally there is a risk of erosion due to the high lubricant velocities at greater sliding speeds. However, the impregnated sinter alloys can be made largely corrosion resistant by the use of a nickel-containing copper alloy with tin and antimony being added to the impregnating alloy, but the automatically resultant coarse structure is of poor fatigue strength. Above all, the necessary additional cover or slide layer will start to crumble prematurely, so that the fatigue strength is not materially improved over the conventional white metal slide layers.
Practice has also demonstrated that, under the higher requirments which these plain bearing materials must meet nowadays with respect to fatigue, corrosion, and wear resistance, the results obtained are not always satisfactory, so that a need remains for a still further improved alloy.